Initial glances at the journal, with its carefree lack of syntax and almost obsessive references to food, led many to suspect a sophisticated, if cruel parody. "Pine trees: nuts. Fig trees: figs (how Alan Bates ate them in Women in Love!)," begins one section. "Olive trees: olives and oils. Sunflowers: more oils. Grapes: my favourite Cervaro. Pasta: spaghetti, taglierini, linguine. Meats: Parma ham. With every smell, I smell food. With every sight, I see food. I can almost hear food. I want to spade the whole lot through my mouth at Mach 2. Basta!"
But suspicions were ill-founded. The duchess's office confirmed that it was, in fact, all her own work. As Frank Johnson, editor of the Spectator, said yesterday: "No one could forge it."
The diary, he said, had been written by the duchess at his request, and was neither a parody, nor ghost-written. "Like all great writers there are depths of meaning," he said, adding, after a pause, "You have Proust, Dostoevsky ... Fergie. If she had a ghost writer it must have been some kind of genius who thinks in her mind."
Indeed, much of it is almost too Fergie-like to be true. She reveals the same talent for self-abasement that emerged from her encounter with television interviewer Ruby Wax, calling herself "ungrateful" and "vain". Her obsession with food, she says, is problematic, as she is meant to be "a paradigm of a weight loser - perhaps the only thing I am allowed to add to being a loser."
But the duchess is nothing if not resourceful: "A brilliant idea comes to mind from reading Hello! I see the Queen of Sweden wearing a T-shirt with a supermodel figure in a bikini printed on it - maybe Weightwatchers won't notice if I put one on at the launch!"
The duchess is keen, however, that we do not forget her charitable credentials, not least her work with the Motor Neurone Disease Association, for whom she has just held a golf tournament.
"MND," she explains, "is the most debilitating, devastating, muscle wasting disease ... Andrew - steadfastly loyal to me and his Scottish Mutual team - started his victorious round dead on time, having already made sure that he had wished his grandmother a happy birthday in the morning."
There are digressions into childhood reminiscence, insights into family ("Andrew and I believe so much in this new Americanism of co-parenting") and the odd pieces of literary twiddle ("The red, earthy, laterite soil was kicked up as Andrew, Beatrice and Eugenie headed off into the distant Tuscan hills on their way to join HMY Brittania")
Perhaps mindful of her audience, the duchess throws in a couple of cultural references: to Dante - and Simba, from Disney's The Lion King. Her new editor is definitely happy with the result. "I knew she would be a good diarist ... I'll ask her to write again," says Mr Johnson. "Although we won't be running one every week."